For providing a flame retardant action for plastics, numerous substances are known which can be employed alone or in combination with further substances which afford similar or supplementary flame retardant properties. Preferably that involves using halogen-free substances to avoid the production and liberation of toxic substances. The known halogen-free flame retardants include those which are based on metal hydroxides, organic or inorganic phosphates, phosphinates or phosphonates with synergistically acting substances or derivatives of 1,3,5-triazine compounds and mixtures thereof.
Inter alia some monomeric, low-molecular flame retardant additives are known, which however because of their severe plasticiser effect in relation to plastics containing the flame retardant lead to significant worsenings of the material properties both in processing and also in use of the plastic. In addition, with such low-molecular flame retardant additives, because of their capability of migration in the plastic material after a certain period of time due to aggregation (less good distribution of the flame retardant additive) or leaching (migration to the surface and possibly issue from the plastic) their flame retardant action decreases.
Polymeric, high-molecular flame retardant additives in contrast generally have only slight plasticizer effects and a low migration capability. In contrast to low-molecular flame retardant additives however they are worse miscible in technical processing with the plastic to be protected, in particular by virtue of their worse melting capability and solubility in the plastic. WO 2009/109347 A1 for example discloses a straight-chain polyfunctional polymer which is obtained by Michael addition of DOPO to an itaconic acid and subsequent polycondensation with ethylene glycol. When that polymer is used in polyesters or polyamides they have a sticky and strongly adhering consistency under usual extrusion conditions of plastics (between 250 and 270° C.), whereby in particular in the loading region clogging and agglutination (blockage) of parts of the extrusion equipment is increasingly to be observed. In addition that polymer already breaks down from temperatures of about 300° C.
WO 2011/080306 discloses the use of such polymers of addition products of DOPO in connection with further flame-retardant components. It is assumed that improved processability of plastics occurs due to a use of smaller amounts of that polymer in conjunction with a further flame-retardant component which in that composition acts synergistically with the polymer. Therefore plastics which contain such synergistic mixtures can be processed in spite of the use of a polymer which is difficult to process, without clogging and metering in an extrusion process.